The storm was centred at 8 a.m. EDT Sunday about 100 miles (165 kilometres) north-northwest of St. Martin and was gradually moving away from the Virgin Islands, the U.S. National Hurricane Center in Miami said. Rafael had top sustained winds of 50 mph (85 kph) and was moving north-northwest at 12 mph (19 kph).

Forecasters said Rafael could become a hurricane by Monday, adding interests in Bermuda should monitor Rafael's progress. The centre's advisory said a tropical storm or hurricane watch may be required for Bermuda sometime Sunday.

A tropical storm warning has been discontinued for Anguilla. Earlier Sunday, a tropical storm watch was discontinued for Puerto Rico.

Rafael could dump rainfall totalling between 3 and 5 inches on some islands and possibly up to 10 inches in isolated spots over the lesser Antilles and the Virgin Islands, raising the threat of flooding, forecasters said. Potentially heavy rains could cause life-threatening flash floods and mudslides, particularly in mountainous terrain, the hurricane centre said.

Forecasters also warned of possibly dangerous surf churned up by Rafael.

Tropical storm-force winds extended outward up to 175 miles (280 kms) from the centre of Rafael, mainly to the northeast and east of the system, forecasters said.